For example with a polymer electrolyte fuel cell, the voltage of each cell is measured (observed) to confirm that normal power generation is being performed with each cell, or to perform flow control of the reaction gases (fuel gas and oxidant gas). When measuring cell voltage, the terminals electrically connected to each cell of the fuel cell are used.
A terminal device (terminal unit) having a plurality of terminals corresponding to a plurality of cells is known for measuring cell voltage for a plurality of cells of a fuel cell.